Crystallization Behavior and Crystal Orientation of Poly(ε-caprolactone) Homopolymers Confined in Nanocylinders: Effects of Nanocylinder Dimension

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Abstract

The crystallization behavior and crystal orientation of poly(ε-caprolactone) (PCL) homopolymers and PCL blocks spatially confined in identical nanocylinders have been investigated using differential scanning calorimetry (DSC) and two-dimensional wide-angle X-ray diffraction (WAXD) as a function of cylinder diameter D. The PCL homopolymers confined in nanocylinders were prepared using microphase separation of PCL-block-polystyrene (PCL-b-PS) copolymers with a photocleavable o-nitrobenzyl group (ONB) between PCL and PS blocks and the subsequent cleavage of ONB by irradiating UV light. The time evolution of PCL crystallinity χPCL showed a first-order kinetics for both PCL blocks and PCL homopolymers confined in all the nanocylinders investigated. However, the D dependence of crystallization rates for PCL blocks was more drastic than that for PCL homopolymers, and consequently various D-dependent interrelations were observed between crystallization rates of PCL blocks and PCL homopolymers. The crystal orientation was also dependent on D; the b-axis of PCL crystals oriented parallel to the cylinder axis both for PCL blocks and PCL homopolymers confined in the nanocylinder with D = 13.0 nm, whereas the (110) plane of PCL crystals was normal to the cylinder axis in the nanocylinders with D ≥ 14.9 nm. The difference in the degree of crystal orientation was not detected between PCL blocks and PCL homopolymers confined in nanocylinders with D ≥ 14.9 nm.

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